No. 



1. 



No. 



2. 



No. 



3. 



In. 



Lin. 



In. 



Lin. 



J«. 



Lin 



2 



8 



2 



8 



2 



7 



3 



6 



3 



3 



o 



6 



3 



5 



3 



2 



2 



6 



5 



6 



5 



8 



4 







5 







14 







10 



6 



1 



3* 



1 



7 



1 



4 



2 







2 



2 



2 



6 



WEALDEN FORMATIONS. 17 



instructive series, or in the more anterior and detached caudal vertebrae. The follow- 

 ing are the dimensions of the detached anterior caudal (No. 1), and of the first (No. 2) 

 and last (No. 3) of the series of six : 



Antero-posterior diameter of centrum 

 Vertical diameter of articular surface 

 Transverse diameter of articular surface 

 From under part of centrum to upper end of 



posterior zygapophysis .... 

 From upper end of posterior zygapophysis to | 



the summit of spine . . . .■> 



Antero-posterior diameter of base of spine 

 Antero-posterior diameter of summit of spine 



The chevron bones, of which three are preserved in the slab containing the six 

 caudal vertebras, Tab. VIII, h, h, exhibit the perforated character, ib. h, which distin- 

 guishes them from those of the Cetiosaurus and of all existing Crocodiles and Lizards, 

 not excepting the Iguana, in which the hgemapophyses are anchylosed at their distal 

 or spinal end only, and remain separate and articulated to two distinct surfaces, at 

 their proximal ends. The length of the superior and inferior vertebral spines, and the 

 shortness of the transverse processes, prove the form of the tail to have been flattened 

 laterally, and of great breadth in the vertical direction, at its basal portion at least. 



The bases of the neurapophyses, n, n, are nearly co-extensive lengthwise with the 

 centrum, c, and expand transversely so as nearly to meet where they rest upon the 

 centrum, but they do not quite circumscribe the neural canal. They contract rapidly 

 in antero-posterior extent, forming the notches of the conjugational foramina, or nerve- 

 outlets, of which the posterior notch is the deepest. 



Detached Caudal Vertebra of the Iguanodon. Tab. IX. 



The characteristic and well preserved caudal vertebra obtained by Mr. G. B. 

 Holmes, from the Stammerham quarry of Wealden Stone, near Horsham, Sussex, is 

 represented in different points of view in Tab. IX, two thirds the natural size. 

 Fig. 1 gives a side view, showing the slightly concave almost flat surface of the side of 

 the centrum ; these lateral surfaces converge towards the under surface, the anterior 

 and posterior angles of which are, as it were, truncated for the articulations, k and K, 

 of the confluent bases of the hsemapophyses ; the diapophysis, d, springs out from near 

 the back part of the vertebra, about the line of suture of the centrum c, and neural 



* The anterior basal ridge of this vertebra is broken away. 



